Method and apparatus for the drying of green ceramic and other materials

ABSTRACT

Apparatus for drying green ceramic articles such as high-voltage insulators, includes a drying chamber and an adjacent chamber in which drying air is pre-treated to give a required temperature and humidity. Once the latter has been achieved valves are opened, initially to a small extent, to admit the pre-treated air to the drying chamber.

United States Patent Huthmann 1Marci'1 13, 1973 [5 1 METHOD AND APPARATUS FOR THE [56] References Cited DRYING OF GREEN CERAMIC AND OTHER MATERIALS UNIT ED STATES PATENTS 1,859,613 5/1932 [75] Inventor. 2123b Hutlimann, Laggenbeck, Ger 1,513,932 11/1924 y 2,606,372 8/1952 [73] Assignee: Keller Ofenbau Gmbl-l, Laggen- 2,932,905 4/1960 beck, Germany 3,001,298 9/1961 1 Filed: 101 1971 Primary ExaminerCarrol1 B, Dority, Jr. [21] APPL No: 114,245 A1torneyMason, Mason & Albright [57] ABSTRACT [30] Foreign Application Priorlty Data Apparatus for drying green ceramic articles such as Feb. 1 l, 1970 Germany ..P 20 06 043.9 highwohage insulators, includes a drying chamber and an adjacent chamber in which drying air is pre-treated [52] U.S. Cl. ..34/72, 34/212, 34/223, to give a required temperature and humidity Om:e the 34/225 latter has been achieved valves are opened, initially to [51] Int. Cl ..F261) 21/06 a ll extent to admit the pre treated air to the y [58] Field of Search ..34/26, 46, 72, 212, 213, 219, mg chamber 1 Claim, 3 Drawing Figures 0 18 10,11 21 3, A l T t I Q a29 0 16 74 72 3 g 77 x r P 1 q II 1 lg; 11 8 1 Ill 11' X\ \I \l l \i {l Z a 6 I l w I 1 1- 5 2219 3 I 1 I I I N v 27 24 I N 1 I H b 7C1 I 1 I 7 I 1 I I 1 1 ll 1 K 2a 25 2s 2 2b PATENIEDHARI 3mm sum 10F 2 F I6. I

PATENTEDHARI 3197s SHEET 2 BF 2 Fla. 3.

METHOD AND APPARATUS FOR THE DRYING OF GREEN CERAMIC AND OTHER MATERIALS BACKGROUND OF THE INVENTION 1. Field of the invention This invention relates to a method of and apparatus for the drying of material to be dried which is very difficult to handle and is of a predominantly ceramic character, in particular porcelain high-voltage insulal tors, glass crucibles or other large moulded articles of ceramic or similar materials, for example made of sinter material or magnetic powder.

2. Description of the prior art Known chamber drying ovens in which porcelain high-voltage insulators are dried, operate with air cir culation and partially with the supply of air through nozzles.

These known ovens do not fulfil the important requirement of making possible no or at least only a little evaporation at the commencement of drying.

Also over a period of several hours at the commencement of drying, the required initial ambient with very high humidity cannot be achieved and maintained. Particularly with porcelain high-voltage insulators a very slow evaporation rate is necessary initially, since with rapid removal of water the projecting parts dry more quickly than the thicker base parts. Between these parts drying at substantially different rates substantial stresses arise which give rise to the formation of cracks.

Attempts have been made to relieve parts subject to this risk by wrapping and covering up. In order however to achieve an acceptable production quality, a long drying period is necessary, which may amount to as much as 4 weeks. This kind of drying is therefore very uneconomic.

Moreover, there arises with the known drying methods the disadvantage that the air circulating in the drying space cannot be exchanged without the humidity being substantially reduced. In order to overcome this, the vapor is directed into the drying space. This feature under consideration, as a necessary aid, leads to the formation of fog and to condensation on the material to be dried. Moreover, the vapor deposits itself as water of condensation on the walls of the chamber and therefore becomes practically valueless.

An object of the present invention is to provide a method and apparatus for the drying of materials or articles to be dried predominantly of a ceramic character, which materials are very difficult to handle, in particular porcelain high-voltage insulators, in which the drying air is made suitable for the material or articles to be dried appropriate to the drying ambient so that a favorable drying period is achieved.

SUMMARY OF THE INVENTION According to the present invention there is provided a method of drying materials comprising the steps of placing the material to be dried in a drying space, circulating drying air in a pre-treatment space separate from the drying space to bring the air to an appropriate temperature and humidity, and admitting the pre-treated drying air to the drying space at a controlled rate.

In the apparatus in accordance with the invention to carry out this method there is provided preferably two fans in the air pre-treatment chamber and adjacent each fan a duct for the removal of surplus wet air or the admission of fresh air. Preferably both ducts are closable by valves.

Advantageously between the drying chamber and the air pre-treatment chamber there is arranged a separating wall in which are provided adjustable closure valves.

By means of the method and apparatus in accordance with the invention the necessary drying time while avoiding the formation of drying cracks is substantially reduced since the drying ambient, before the commencement of drying, can be regulated as to temperature, humidity and amount of air movement corresponding to physical requirements of the material.

Moreover the drying stresses are reduced, so that as a result of the drying method in accordance with the invention, smaller differences arise in the dampness of the material both inside of and outside of the material to be dried.

Further the independent control of the drying ambient renders possible a physically favorable drying with a substantially reduced drying period.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinal section through the apparatus in accordance with the invention;

FIG. 2 is a section on the line IIII of FIG. 1;

FIG. 3 is a section on the line IIIIII of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT A drying apparatus is denoted by the reference numeral l which comprises outer walls 1a and lb. Transverse walls 1c and 1d close the drying chamber at both sides. Inlets are provided in the transverse wall Id.

In the lower part of the drying chamber 1 there is a drying space 2, which is divided into two compartments 2a and 2b, to which carriages laden with material to be dried are inserted. Above the drying space 2 there is arranged an air pre-treatment space 3 which is separated from the drying space 2 by a separating wall 4.

The separating wall 4 has two air entry holes 5 and 6 in the region of the drying chamber outer walls 1a and 1b which can be closed by means of flap valves or slides 7 and 8. Furthermore, air outlet holes 9 are provided at the center of the separating wall 4.

Above the air outlet holes 9 there are two spaced fans 10 and 11, which are mounted between respective sides of air ducts l2 and 13.

The air ducts l2 and 13 serve for the removal of excess wet air or for the supply of fresh air. The air ducts l2 and 13 extend from the transverse wall 10 to the opposite transverse wall 1d and are provided with openings 14 and 15 which are closable by means of flap valves 16 and 17.

By the particular arrangement of fans 10 and 11 and the air ducts l2 and 13 there are defined in the air pretreatment space 3 ambient control passages 18 and 19. When the valves 7 and 8 are closed a separate air flow circuit is produced in which the air supplied by the fans into the passage 18 is pressurized and from there is returned via the passage 19 to the fans 10 and 11.

In the ambient control passage 18, air heaters 20 and 21 are provided, which bring the air to the required temperature while the ambient control passage 19 contains air humidifiers 22, 23 which impart to the heated air the correct air humidity.

To improve the air flow in the drying space 2 guide walls 24, 25, 26-and 27 provided with openings are mounted therein and the air pre-treatment space 3 has guide blades 28 and 29 mounted therein.

The manner of operation of the apparatus in accordance with the invention is as follows:

As soon as the carriage carrying the material to be dried is inserted into the compartments 2a and 2b of the drying space 2 the drying process commences.

Since it is concerned with large moulded articles sensitive to the drying process in particular porcelain highvoltage insulators, it is necessary that the material to be dried should be subjected to drying air at the appropriate humidity and temperature which allows only the smallest possible evaporation at the beginning of drying.

For this purpose the closure valves 7 and 8 remain closed initially so that no air circulation takes place in the drying space 2.

The drying air is circulated initially separately in the air pre-treatment space in such a manner that it is brought to the required during temperature and air humidity as a result of flow through the air heaters 20 and 21 and the air humidifiers 22, 23, for example a temperature of 60C and 90percent humidity. By the pretreatment of the drying air the removal of moisture in the moulded article is effected by evaporation so that the moisture is dispersed in the form of a gas in the drying air. Mist and drip formation are prevented by the baffle plates and the air humidifiers 22 and 23 and by the heating of the air.

The air humidifiers which are used are well known and can be obtained commercially.

As soon as the drying air has been pre-treated so that it is suitable for use as the drying ambient of the drying process, the closure valves 7 and 8 are opened so far that initially only a small part of the drying air can enter through the air inlet valves and 6 into the drying chamber 2, where it flows over and around the drying material and is removed through the air outlet holes 9 from the drying space 2 and is returned to the air pretreatment space 3.

At the commencement of the drying process the dry I ing space 2 is only ventilated to a small extent, so that only a small air movement takes place, and thus water is only gradually removed from the material to be dried. The heat penetrates slowly to the core and drives the water outwardly.

With the passage of time the valves 7 and 8 are further opened so that at the end of the drying process the drying air passes unhindered through the air inlet valves 5 and 6 and can pass through the drying space 2 with full force.

By the provision of control devices regulation of the physical parameters of the drying ambient can be undertaken automatically.

I claim:

1. Apparatus for drying materials comprising means defining a drying space for the reception of the material,

means defining an air pre-treatment space separate from the drying space and including passageways for circulating air selectively only within the pretreatment space,

control valve means controlling communication between the pre-treatment space and the drying s ace,

hea er means within the pre-treatment space,

humidifying means within the pre-treatment space,

two fans disposed in the pre-treatment space, for circulating air through the said passageways and within the pre-treatment space whereby the temperature and humidity can be brought to the required values by the heater means and the humidifying means prior to communication being established by the control means between the pretreatment space and the drying space,

ducts for removing excess wet air and for admitting fresh air respectively to the pre-treatment space, and

valves controlling flow through said ducts,

said ducts being disposed laterally of the fans and serving to define said passageways in conjunction with the means defining the air pre-treatment space.

* III 

1. Apparatus for drying materials comprising means defining a drying space for the reception of the material, means defining an air pre-treatment space separate from the drying space and including passageways for circulating air selectively only within the pre-treatment space, control valve means controlling communication between the pretreatment space and the drying space, heater means within the pre-treatment space, humidifying means within the pre-treatment space, two fans disposed in the pre-treatment space, for circulating air through the said passageways and within the pre-treatment space whereby the temperature and humidity can be brought to the required values by the heater means and the humidifying means prior to communication being established by the control means between the pre-treatment space and the drying space, ducts for removing excess wet air and for admitting fresh air respectively to the pre-treatment space, and valves controlling flow through said ducts, said ducts being disposed laterally of the fans and serving to define said passageways in conjunction with the means defining the air pre-treatment space. 